During a typical process of manufacturing a semiconductor device, a gate oxide layer 102 is formed on a semiconductor substrate 100. A doped polysilicon layer 104a used as a gate electrode is formed on the gate oxide layer 102 as shown in FIG. 1. A liner layer 106 and a spacer 108 are formed on the sidewalls of the doped polysilicon layer 104a. In addition, an LDD source/drain 114 having a lightly doped region 110 and a heavily doped region 112 is formed under the liner layer 106 and the spacer 108.
A P-type polysilicon layer is widely used for the gate electrode in a semiconductor device. The P-type polysilicon layer 104a is, as shown in FIG. 2, usually formed by a doping process using boron 116 with a mask pattern 109 having an opening exposing only the polysilicon layer 104. Alternatively, as shown in FIG. 3, the P-type polysilicon layer 104a may be formed by a doping process using boron 116 after forming an isolation layer 101, a gate oxide layer 102, and a polysilicon layer 104 on the semiconductor substrate 100.
The doping process using boron is performed by an in-situ process in a furnace, or by ion implantation of boron ions or BF3 ions. In FIG. 1 to FIG. 3, the same reference numerals indicate the same members.
The boron used for forming a P-type polysilicon layer is volatile, and thus, when the thickness of the P-type polysilicon layer is reduced, the concentration of the boron cannot be precisely obtained as desired.
To clarify multiple layers and regions, the thickness of the layers are enlarged in the drawings. Wherever possible, the same reference numbers will be used throughout the drawing(s) and accompanying written description to refer to the same or like parts. As used in this patent, stating that any part (e.g., a layer, film, area, or plate) is in any way positioned on (e.g., positioned on, located on, disposed on, or formed on, etc.) another part, means that the referenced part is either in contact with the other part, or that the referenced part is above the other part with one or more intermediate part(s) located therebetween. Stating that any part is in contact with another part means that there is no intermediate part between the two parts.